Signal transmission system



PL 1941- J. H. BQLLMAN 2,254,205

SIGNAL TRANSMISSION SYSTEM Filed April 3, 1940 2 Sheets-Sheet l BULGENETWORK NETWORK SLOPE NETWORK NETWORK b l/WEA/TOR By J. H. BOLLMAN N ATTORNEV Sept. 2, 1941. J. H. BOL LMAN S IGNAL TRANSMIS S I ON SYSTEMFiled April '3, 1940 2 Sheets-Sheet 2 lAl VV lX/VE/V TOR 1 h. BOLLMAN Ar TORNFY Patented Sept. 2, 1941 SIGNAL TRANSMISSION SYSTEM John H.Bollman, Rutherford, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationApril 3, 1940, Serial No. 327,574

11 Claims.

This invention relates to signal transmission systems and particularlyto signal transmission systems having control circuits for governing theloss on transmission lines.

One object of the invention is to provide a signal transmission systemcomposed of a number of transmission lines each having carrier and pilotchannels thereon that shall control the flat ain and the attenuationcharacteristic on each transmission line according to the strengths ofpilot currents on the respective lines and that shall control the fiatgain and the attenuation characteristic on a transmission line accordingto the strengths of pilot currents on other lines in case of failure ofthe pilot current control associated therewith.

Another object of the invention is to provide control circuits for asignal transmission system composed of a number of transmission lineseach having signal and pilot channels and an amplifier and bulge andslope networks thereon that shall control the amplifier and the bulgeand slope networks on each transmission line according to the strengthsof pilot currents on the respective lines and that shall control theamplifier and the bulge and slope networks on a transmission lineaccording to the strengths of pilot currents on other lines in case offailure of the pilot current control associated therewith.

A further object of the invention is to provide control circuits for asignal transmission system composed of a number of transmission lineseach having carrier and pilot channels and an amplifier and bulge andslope networks thereon that shall control low frequency circuits togovcm the amplifier and the bulge and slope networks on eachtransmission line according to the strengths of pilot currents on therespective lines and that shall control the low frequency circuitsgoverning the amplifier and bulge and slope networks on a transmissionline according to the strengths of pilot currents on other lines in caseof failure of the low frequency circuits associated therewith.

Transmission systems, for example carrier cable systems, are providedwith fiat gain and twist pilot wire regulators which are located atintervals along the cable. 'It has been found that certain over-alllosses occur on the pairs of conductors making up a cable which are notcorrected for by the distributed fiat gain and twist regulators. 1

According-to the invention disclosed in the patent to H. K. Krist, No.2,246,307, issued June are controlled by pilot currents, are provided tocompensate for the over-all losses. tion regulators not only adjust thefiat gain but also the slope and bulge of the line attenuationcharacteristic. In the invention disclosed in the H. K. Krist patent,No. 2,246,307, a gain control amplifier, a slope network and a bulgenetwork are placed on each pair of conductors in a cable at the terminalor deviation station. Each pair of conductors in the cable is not onlyprovided with carrier channels but also with pilot channels. The pilotcurrents on a pair of conductors respectively control the amplifier, theslope network and the bulge network on the associated pair ofconductors.

According to the present invention, provision is made for governing theamplifier, the slope network or the bulge network on a pair ofconductors according to the strengths of pilot currents on other pairsof conductors in case of failure of the pilot current control meansassociated with the pair of conductors. Thus, in case of failure of thepilot current regulating circuits associated with one pair of conductorsthe amplifier and the bulge and slope networks Will be operatedapproximately to correct operating positions by regulating circuitsassociated with other pairs of conductors.

In the arrangement employed to describe the invention, two pairs ofconductors in a carrier cable system are provided with an amplifier andslope and bulge networks. Each pair of conductors is provided not onlywith carrier channels but also with three pilot channels. The threepilot currents on each pair of conductors respectively govern the flatgrain amplifier, the slope network or equalizer, and the bulge networkor equalizer. A'pilot filter which selects the three pilot currents onthe pair of conductors is connected'to the conductors at a point beyondthe amplifier and the bulge and slope networks. The selected pilotcurrents are amplified and then supplied to three auxiliary filterswhich separate the three pilot currents that govern the operation of thefiat gain amplifier, the slope network and the bulge network. 1

The pilot current which is selected by the auxiliary filter foroperating the flat gain amplifier is supplied to a bridge in the formof' a voltage doubler rectifier. The output from the voltage doublerrectifier, opposed by a constant potential, supplies negative bias foroperating a control space discharge device. The control space dischargedevice'is energized by a direct-current .17, 1941, terminal or deviationregulators, which source and a source of alternating current. The

The deviacontrol space discharge device governs the operation of aheater coil for controlling a resistance connected across the negativefeedback circuit in the fiat gain amplifier. The resistance elementcontrolled by the heater coil has a negative temperature coefficient ofresistance and preferably is of the type disclosed in the E. F. Dearbornapplication, Serial No. 280,692, filed June 23, 1939. The resistanceelement in the feedback circuit of the flat gain amplifier is socontrolled as to oppose any change in the strength of the pilot currentfrom normal value. If the pilot current tends to increase in strength,the gain of the feedback amplifier is reduced to bring the strength ofthe pilot current back to normal value.

The output from the control space discharge device is not only connectedto the heater coil for governing the resistance in the feedback circuitof the flat gain amplifier but is also connected through 'esistanceelements to equalizing bus conductors. Other control space dischargedevices for governing the heater coils to govern other flat gainamplifiers in other pairs of conductors are also connected to theequalizing bus conductors by resistance elements. Thus, in caseof,failure of the circuit governing the heater coil for governing a flatgain amplifier on a pair of conductors, current will be supplied fromthe equalizing bus conductors for operating the heating coil to anapproximate value for main taining the strength of the pilot current onthe pair of conductors at approximately correct strength.

The auxiliary filter which selects the pilot A current for operating theslope network is connected to a voltage doubler rectifier forcontrolling the operation of a control space discharge device. Theoutput from the voltage doubler rectifier is opposed by a standardpotential source to effect a more than proportional change for anychange in the strength of the pilot frequency current. The control spacedischarge device is energized not only by direct current but also by alow frequency power current. The output from the control space dischargedevice is connected to a heater coil for governing a resistance in theslope network. The resistance in the slope network controlled by theheater coil has a negative temperature coeiicient of resistance and maybe of the same type as that employed for controlling the feedbackcircuit of the fiat gain amplifier. The control space discharge deviceis not only connected to the heater coil for governing the operation ofthe slope network but is also connected through resistance elements toequalizing bus conductors. The equalizing bus conductors are connectedsimilarly to other control space discharge devices associated with otherpairs of conductors so that in case of failure of the control for oneslope network the control may be taken over by the equalizing busconductors.

The auxiliary filter which selects the pilot current for operating thebulge network is connected to a voltage doubler rectifier which in turncontrols the negative bias impressed on the grid of a control spacedischarge device. The output from the voltage doubler rectifier isopposed by a constant potential source to effect a more thanproportional change in the operation of the control space dischargedevice than the changes in strength on the pilot current. The controlspace discharge device'is energized by a direct-current source and by asource of alternating current which, if so desired, may be a commercialsource of power. The output circuit of the control space dischargedevice is connected to a heater coil for operating a resistance elementhaving a negative temperature coefficient of resistance. The resistanceelement is included in the bulge network on the pair of conductors. Thisresistance element having a negative temperature coefficient ofresistance may be of the same type as that employed in controlling thefeedback circuit of the fiat gain amplifier. The output circuit of thecontrol space discharge device is not only connected to the heater coilfor governing the bulge network but is also connected through resistanceelements to equalizing bus conductors. The equalizing bus conductors areconnected through resistance elements to other control space dischargedevices associated with the bulge networks on other pairs of conductors.Thus in case of failure of the control circuits for operating a bulgenetwork on one pair of conductors, the control of this network may betaken over by the equalizing bus conductors connected to the heater coilwhich governs the operation of the network.

In the accompanying drawings, Fig. 1 when placed above Fig. 2 disclosesa system constructed in accordance with the invention.

Referring to the drawings, a terminal or deviation station I is shownconnected to a pair of conductors in a carrier cable system having inputconductors 2 and 3 and output conductors 4 and 5. The input conductors 2and 3 are con nected by a transformer 6 to a flat gain amplifier l ofany suitable type. The fiat gain amplifier I is provided with a negativefeedback circuit having series resistance elements 8 and 9 and a shuntresistance element It. The shunt resistance element I0 has a negativetemperature coefficient of resistance and may be of the type disclosedin the above-mentioned application of E. F. Dearborn, Serial No.280,692. The resistance element I0 is controlled by a heater coil H in amanner to be hereinafter described.

The amplifier I is connected to a slope equalizer or network [2 whichmay be of the type disclosed in the H. W. Bode Patent 2,096,027, October19, 1937 or in the E. L. Norton Patent 2,019,624, November 5, 1935. Theslope network I2 is controlled by a resistance element l3 having anegative temperature coefficient of resistance. This resistance elementl3 may be of the, same type as the resistance element :0 employed tocontrol the flat gain amplifier 1. A heater coil I4 is provided forgoverning the operation of the resistance element It in a manner to behereinafter set forth.

The slope network I2 is connected to a bulge equalizer or network I5which may be on the type disclosed in the S. Darlington Patent2,153,743, April 11, 1939. The bulge network I5 is governed by aresistance element l0 having a negative temperature coefficient ofresistance. The resistance element It may be of the same type as theresistance element It employed to control the flat gain amplifier 1. Theresistance element I6 is governed by a heater coil H in a manner to behereinafter set forth. The bulge network 15 is connected by an amplifierl8 and a transformer I9 to the output conductors i and 5.

The pair of conductors not only is provided with carrier channels butalso with three pilot channels. A pilot filter 20 is connected to thepair of conductors. beyond the amplifierv 8 for selecting the threepilot currents. The pilot filter comprises two transformers 2| and 22, acrystal 23, a condenser 24 and a resistance element 25 connected acrossthe secondary winding of the transformer 22. nected to the input circuitof an amplifier 26 in the form of a pentode tube. The amplifier 26comprises an anode 21, a control grid 28 and a cathode 29. Negative biasfor the control grid 28 is supplied by the potential drop across aresistance 30. Potential for the anode 21 is supplied from abattery 3|through a resistance element 32 and auxiliary filters 33, 34 and 35. Theauxiliary filters 33, 34 and 35 respectively select the three pilotcurrents which are employed to control the fiat gain amplifier 1,'theslope network l2 and the bulge network l5. vThe filter 33 comprises atransformer 36 and an adjustable condenser 31. The auxiliary filter 34comprises a transformer 38 and an adjustable condenser 39. The auxiliaryfilter 35 comprises a transformer 46 and an adjustable condenser 4|.

The secondary winding of the transformer 36 which forms a part of theauxiliary filter 33 is connected to two opposite vertices of a bridgecircuit 42. The bridge circuit 42 is in the form of a voltage doublerrectifier of the type-disclosed in the patent to D. M. Terry, 2,084,115,June 15, 1937. The voltage doubler rectifier comprises two condensers 43and 44 and two rectifiers 45 and 46 which are preferably of the copperoxide type. The output vertices of the voltage doubler rectifier areconnected across a resistance element 41. The potential drop across theresistance element 41 is employed to govern the operation of a controlspace discharge device 48 in the form of a pentode tube. The device 48comprises an anode 49, a control grid 50 and a cathode 5|.

control grid 50 is opposed by a portion of the potential drop across aresistance element 52. The resistance element 52 is connected to abattery 53 through a resistance 54. The potential drop across a portionof the resistance element 52 opposes the potential drop across theresistance element 41 to effect a more than proportional change in theoperation of the control space discharge device 48 for changes instrength of the pilot current selected by the auxiliary filter 33.

The anode 49 of the device 43 is supplied with direct potential from thebattery 3| by a circuit which extends from one terminal of the battery3| through a choke coil 55, secondary winding of the transformer 56,primary winding of the transformer 51, anode 49 and cathode 5| to theother terminal of the battery 3|. A source of low frequency current 58is connected to the plate circuit of the device 48 by means of thetransformer 56. The alternating-current circuit through the device 48 iscompleted by a condenser 59.

The low frequency output current from the device 48 is connected by thetransformer 51 to the heater coil The heater coil II, as before setforth, controls the temperature of the resistance element |0 which has anegative temperature coefficient of resistance. The resistance. l0governs the feedback circuit for the fiat gain amplifier 1.

v Ifthe pilot current on the pair of conductors which controls the hatgain amplifier 1 rises above normal value, the rectified current im- Thepotential drop across the resistance element 41 which is impressed onthe The pilot filter 29 is conpressed across the resistance 41 increasesto increase the. negative .bias impressed on the control grid 59 of thedevice 48. The low frequency output from the device .48 is reduced toreduce the current supplied to the heater coil II. This reduces thetemperature of the resistance element I0 and accordingly increases theresistance value thereof. An increase in the resistance value of theresistance element l9 decreases the gain of the fiatgain amplifier 1 toreturn the strength of the pilot current governing the fiat gainamplifier to normal value. If the strength of the pilot currentgoverning the fiat gain amplifier 1 falls below normal value, anopposite operation takes place.

The control device 48 is not only connected to the heater coil H by thetransformer 51 but is also connected through resistance elements 60 andBI to a pair of equalizing bus conductors 62. The equalizing busconductors 62 are also connected in a similar manner to the controlspace discharge devices which govern the operation of other flat gainamplifiers on other pairs of conductors. In Fig. 1 of the drawings, theconnection to another control device is indicated. A transformer 63which is similar to the transformer 51 connects a control device, notshown, not only to a heating coil 64 for governing the feedback on anamplifier for another pair of conductors, but also through resistanceelements 65 and 66 to the equalizing bus conductors 62. In case offailure of the low frequency current supplied by the transformer 51 tothe heater coil H for governing the flat gain amplifier 1, it isapparent control current will be supplied to the heater coil H from theequalizing bus conductors 62 through the resistance elements 69 and 6|.Thus; in case of failure of the low frequency control circuits for theheater coil governing an amplifier, it is apparent control of theamplifier will be effected from low frequency control circuitsassociated with other pairs of conductors. The auxiliary filter 34 whichselects the pilot current for governing the slope network I2 isconnected by the transformer 38 to two vertices of a voltage doublerrectifier 61. The voltage doubler rectifier 61 is similar inconstruction and operation to the voltage doubler rectifier 42. Theoutput voltage is impressed across a resistance element 68 whichcontrols the negative grid bias impressed on a control space dischargeddevice69. The device 69 is in'the form of a pentode tube the same as thecontrol space discharge device 49.and comprises an anode 15, a controlgrid 1| and a cathode 12. The negative bias obtained by the potentialdrop across the resistance element 68 which is impressed on the controlgrid 1| is opposed by the potential drop across a portion of aresistance element 13. The

resistance element 13 is in circuit with the battery 53 in the samemanner as the resistance element 52. The device 69 is energized not onlyby the battery 3| but also by the low frequency source of power 58.

A transformer 14 connects the output circuit of the device 69 to theheater coil l4 which controls the resistance element |3 in the slopenetwork |2. The transformer 14 also connects the output from the device69 through resistance elements 15 and 16 to equalizing bus conductors11. The equalizing bus conductors 11 are also connected in the samemanner to the control means for other slope networks associated withother pairs of conductors. One connectionto another slope network isindicated in Fig. 1 of the bulge of the transmission attenuationcharacteristic on each pair of conductors, means comprising a lowfrequency circuit connected to each of said slope and bulge networks forgoverning the operation thereof, means for respectively controlling thelow frequency circuits associated with the slope network and the bulgenetwork of a pair of conductors by two pilot currents on that pair ofconductors, and means for connecting in parallel the low frequencycircuits connected to all said slope networks and for connecting inparallel all the low frequency circuits connected to the bulge networks.

6. In a signal system, a plurality of pairs of conductors each havingcarrier currents and pilot currents thereon, a network for changing theattenuation characteristic and an amplifier on each of said pairs ofconductors, means comprising a low frequency circuit connected to eachof said amplifiers and networks for governing the operation thereof,means for respectively controlling the low frequency circuits associatedwith the amplifier and network of a pair of conductors, and means forconnecting in parallel the low frequency circuits connected to all saidamplifiers and for connecting in parallel all the low frequency circuitsconnected to the networks.

7. In a signal system, a plurality of pairs of conductors having carriercurrents and three pilot currents on each of said pairs of conductors,an amplifier and slope and bulge networks on each of said pairs ofconductors, means comprising a low frequency circuit connected to eachof said amplifiers and networks for governing the operation thereof,means for respectively controlling the three low frequency circuitsassociated with the amplifier and networks of a pair of conductors bythe three pilot currents on that pair of conductors, and means forconnecting in parallel the low frequency circuits connected to all saidamplifiers for connecting in parallel all the low frequency circuitsconnected .to the slope networks and for connecting in parallel all thelow frequency circuits connected to the bulge networks.

8. In a signal system, a plurality of pairs of signal conductors havingcarrier currents and three pilot currents on each of said pairs ofconductors, an amplifier and slope and bulge networks on each of saidpairs of conductors, a control thermistor associated with each of saidamplifiers and networks, a separate low frequency circuit forcontrolling each of said thermistors, means controlled by the pilotcurrents on each pair of conductors for respectively governing the lowfrequency circuits connected to the thermistors of the amplifier andnetworks for that pair of conductors, means for connecting all the lowfrequency circuits associated with said amplifiers in parallel throughresistance elements, for connecting all the low frequency circuitsassociated with said slope networks in parallel through resistanceelements and for connecting all the low frequency circuits associatedwith said bulge networks in parallel through resistance elements.

9. A cable having a plurality of pairs of conductors, a number of saidpairs of conductors having carrier currents and three relatively highfrequency currents thereon, an amplifier and slope and bulge networks oneach of a number of said pairs of conductors, a circuit having a lowfrequency current thereon for each amplifier and network on each of saidnumber of pairs of con ductors, and means for respectively controllingthe low frequency circuits associated with the amplifier and networks oneach pair of conductors by the three pilot currents on each pair ofconductors to respectively govern the fiat gain and slope and bulge ofthe attenuation characteristics of the cable pairs of conductors, andmeans for adjusting the amplifier, slope network or bulge network of apair of conductors according to adjustment of similar apparatus on otherpairs of conductors in case of failure of the low frequency circuitcontrolling the amplifier, slope network or bulge network.

10. A cable having a plurality of pairs of conductors, each of saidpairs of conductors having carrier currents and three relativelyhighfrequency pilot currents thereon, an amplifier and slope and bulgenetworks on each of said pairs of conductors, means comprising circuitshaving low frequency current thereon for separately governing theamplifier, the slope network and the bulge network on each of said pairsof conductors to control respectively the flat gain, the slope of theattenuation characteristic and the bulge of the attenuationcharacteristic on each of said pairs of conductors, means controlled bythe three pilot currents on a pair of conductors for respectivelygoverning the strengths of the low frequency currents controlling theamplifier, the slope network and the bulge networks of the pair ofconductors to maintain the energy levels of the different frequencycurrents on the pair of conductors the same at a desired level, and

means for connecting together the low frequency circuits governing theamplifiers of all pairs of conductors to insure control of an amplifierin case of failure of the low frequency current effecting controlthereof for connecting together the low frequency circuits governing theslope networks of all pairs of conductors to insure control of a slopenetwork in case of failure of the low frequency current eifectingcontrol thereof and for connecting together the low frequency circuitsgoverning the bulge network of all pairs of conductors to insure controlof a bulge network in case of failure of the low frequency currenteffecting control thereof.

11. In a signal system, a plurality of pairs of signal conductors havingcarrier and pilot currents on each pair of conductors, a plurality ofcontrol means on each pair of conductors for respectively governing anumber of different characteristics of the transmitted currents, anumber of circuit means respectively controlled by the pilot currents ona pair of conductors for separately governing the control means on thepair of conductors, and means in case of failure of the control meansgoverning a characteristic of the transmitted current on a pair ofconductors for governing the control means by circuit means associatedwith other pairs of conductors.

JOHN H. BOLLMAN.

